refactor(search): address PR #750 round 2 review feedback

Implements fire-and-forget eviction (ADR-019 §"Lazy eviction"): the
search response no longer waits on Qdrant deletes, instead spawning
evict() on a long-lived lifespan-owned task group. Falls back to inline
eviction in modes without vector sync and in unit tests.

Also: harden _verify_news_items against non-numeric ids (fail open
instead of crashing the verifier); document the get_file_info None-on-404
contract; add INDEXED_DOC_TYPES single source of truth in vector/scanner.py
referenced by the CI-guard test; write a Verify-on-Read Latency Budget
section in docs/configuration.md covering the unbounded news.get_items
fetch. Closes the two remaining ADR-019 implementation checklist items.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/configuration.md

@@ -474,6 +474,45 @@ DOCUMENT_CHUNK_OVERLAP=100
 
 **Important**: Changing chunk size requires re-embedding all documents. The collection naming strategy (see "Qdrant Collection Naming" above) helps manage this by creating separate collections for different configurations.
 
+### Verify-on-Read Latency Budget
+
+Every semantic search request runs an access-control verification pass over its
+results before returning them, to filter out documents the user can no longer
+access (deleted, unshared, permissions changed). See
+[ADR-019](ADR-019-verify-on-read-for-semantic-search.md) for the full design.
+
+This adds Nextcloud round-trips to the search path that operators should be
+aware of:
+
+- **Per-search cost**: one Nextcloud round-trip per *unique* `(doc_id, doc_type)`
+  in the result set. Chunking means a 10-result page typically references 3-5
+  unique documents, so verification adds 3-5 round-trips. With the default
+  20-way concurrency this is one parallel batch — usually under 100 ms on a
+  healthy connection.
+- **Concurrency**: all verifications fan out under a shared semaphore
+  (`DEFAULT_VERIFICATION_CONCURRENCY = 20` in `search/verification.py`). The
+  limit is not currently exposed as an env var; if production workloads
+  saturate Nextcloud, consider opening an issue to make it tunable.
+- **News API caveat**: the News app has no per-item endpoint, so the news
+  verifier issues a single `news.get_items(batch_size=-1, get_read=True)` call
+  per search that contains any news result, then intersects locally. The
+  payload is **unbounded** — for users with very large feed backlogs this can
+  dominate verification latency. Disabling News in the indexer or running with
+  a smaller backlog mitigates this; per-item paginated verification is tracked
+  as a future improvement.
+- **Eviction**: when verification finds a definitive miss (404 / 403), the
+  corresponding Qdrant points are deleted in the background on a lifespan-owned
+  task group — fire-and-forget, does **not** block the search response.
+  Eviction failures are logged but never propagated; the next query will
+  re-verify and re-attempt (self-healing).
+- **Failure modes**: transient errors (5xx, network) keep results visible
+  (fail open) so a flaky link does not silently shrink result pages; only
+  *definitive* 404 / 403 drops them.
+
+If verification ever needs to be disabled (debugging, benchmarking), the
+`evict_on_missing=False` flag on `verify_search_results()` skips eviction
+without changing what is returned to the caller.
+
 ### Environment Variables Reference
 
 | Variable | Required | Default | Description |